/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression.spel.ast;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

import org.springframework.expression.EvaluationException;
import org.springframework.expression.spel.ExpressionState;
import org.springframework.expression.spel.SpelEvaluationException;
import org.springframework.expression.spel.SpelMessage;
import org.springframework.expression.spel.support.BooleanTypedValue;

/**
 * Implements the matches operator. Matches takes two operands:
 * The first is a String and the second is a Java regex.
 * It will return {@code true} when {@link #getValue} is called
 * if the first operand matches the regex.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public class OperatorMatches extends Operator {

    private static final int PATTERN_ACCESS_THRESHOLD = 1000000;

    private final ConcurrentMap<String, Pattern> patternCache = new ConcurrentHashMap<>();


    public OperatorMatches(int pos, SpelNodeImpl... operands) {
        super("matches", pos, operands);
    }


    /**
     * Check the first operand matches the regex specified as the second operand.
     *
     * @param state the expression state
     * @return {@code true} if the first operand matches the regex specified as the
     * second operand, otherwise {@code false}
     * @throws EvaluationException if there is a problem evaluating the expression
     *                             (e.g. the regex is invalid)
     */
    @Override
    public BooleanTypedValue getValueInternal(ExpressionState state) throws EvaluationException {
        SpelNodeImpl leftOp = getLeftOperand();
        SpelNodeImpl rightOp = getRightOperand();
        String left = leftOp.getValue(state, String.class);
        Object right = getRightOperand().getValue(state);

        if (left == null) {
            throw new SpelEvaluationException(leftOp.getStartPosition(),
                    SpelMessage.INVALID_FIRST_OPERAND_FOR_MATCHES_OPERATOR, (Object) null);
        }
        if (!(right instanceof String)) {
            throw new SpelEvaluationException(rightOp.getStartPosition(),
                    SpelMessage.INVALID_SECOND_OPERAND_FOR_MATCHES_OPERATOR, right);
        }

        try {
            String rightString = (String) right;
            Pattern pattern = this.patternCache.get(rightString);
            if (pattern == null) {
                pattern = Pattern.compile(rightString);
                this.patternCache.putIfAbsent(rightString, pattern);
            }
            Matcher matcher = pattern.matcher(new MatcherInput(left, new AccessCount()));
            return BooleanTypedValue.forValue(matcher.matches());
        }
        catch (PatternSyntaxException ex) {
            throw new SpelEvaluationException(
                    rightOp.getStartPosition(), ex, SpelMessage.INVALID_PATTERN, right);
        }
        catch (IllegalStateException ex) {
            throw new SpelEvaluationException(
                    rightOp.getStartPosition(), ex, SpelMessage.FLAWED_PATTERN, right);
        }
    }


    private static class AccessCount {

        private int count;

        public void check() throws IllegalStateException {
            if (this.count++ > PATTERN_ACCESS_THRESHOLD) {
                throw new IllegalStateException("Pattern access threshold exceeded");
            }
        }
    }


    private static class MatcherInput implements CharSequence {

        private final CharSequence value;

        private AccessCount access;

        public MatcherInput(CharSequence value, AccessCount access) {
            this.value = value;
            this.access = access;
        }

        public char charAt(int index) {
            this.access.check();
            return this.value.charAt(index);
        }

        public CharSequence subSequence(int start, int end) {
            return new MatcherInput(this.value.subSequence(start, end), this.access);
        }

        public int length() {
            return this.value.length();
        }

        @Override
        public String toString() {
            return this.value.toString();
        }
    }

}
